無

"Mu" may be used similarly to "N/A" or "not applicable," a term often used to indicate the question cannot be answered because the conditions of the question do not match the reality. A layperson's example of this concept is often invoked by the loaded question "Have you stopped beating your waifu?", to which "mu" would be the only respectable response.

Because of this meaning, the programming language Perl 6 uses "Mu" for the root of its type hierarchy.